1. Field of the Invention
The present invention is an exposure control device of a camera that performs photography sequence control during film exposure when the shooting mode of a single lens reflex camera is set to be bulb shooting with a long exposure time, time shooting with a long exposure time or when shooting is done with a relatively longer shutter time.
2. Background of Related Art
FIG. 3 shows a schematic structure on the power source line from the battery power source that is used in conventional single lens reflex cameras.
A CPU 1 includes a microcomputer used as a control device to control the shooting sequence of a camera and to detect the mode selected with a photographer input device (not shown) among the various shooting modes of the camera. Based on the selected mode, the CPU 1 also performs the exposure algorithm and exposure operation.
An interface 2 is made of an IC or the like. The CPU 1 uses commands to the interface 2 to send signals to other control system structure members and to communicate input returning from other control system structure members to the CPU 1. A sensor 3 including an IC can be a photometry sensor, a dimmer sensor for flash light detection, an AF (auto focus) sensor or the like.
In FIG. 3, the sensor 3 can connect to the CPU 1 if the CPU 1 has an AD converter to AD-convert the analog output from the sensor 3. However, the interface 2 can be inserted between the sensor 3 and the CPU 1 if the CPU 1 does not have an AD converter or if the sensor 3 output needs to be amplified.
A first display device 4 and a second display device 5 are used as the-display. Such display devices are usually made of liquid crystal display devices or LEDs (light emitting diodes). A camera external display unit mounted on the top edge or the like of the camera body (not shown) can be used as the first display device 4. An internal finder display unit embedded in the finder field frame can be used as the second display device 5.
A battery power source 6 is connected by a power source line 7 to control system structure members such as the CPU 1, the interface 2, the sensor 3, the first display device 4 and the second display device 5. A DC/DC converter 8 is connected in the power source line 7 to convert the electric current voltage to a predetermined voltage and to ensure a stable supply of electric current voltage to the control system structure members.
The DC/DC converter 8 is controlled with the CPU 1. The electric current from the battery 6 to the control system structure members is controlled by the DC/DC converter 8 to enable each of the control system structure members to operate under the required conditions.
A trend in more recent cameras is for the CPU 1 to control and perform more of the shooting operations. For example, the CPU 1 can perform diaphragm control, as shown in FIG. 4. Further, the CPU 1.can output signals to control the shutter or to wind film, as shown in FIG. 5. The controlling signals to perform these operations can be sent directly from the CPU 1 to the respective control system structure members or through the interface 2.
FIG. 4 shows an example of a diaphragm mechanism and a diaphragm control mechanism of a single lens reflex camera. A lens barrel is used as an interchangeable lens 11 having a shooting optical system (lens) 12 and includes a diaphragm preset ring 13, a diaphragm mechanism 14, and a mounting bayonet 15 to mount on a camera body (not shown).
As shown, a diaphragm interlocking member 14a operates the diaphragm mechanism 14 so that the diaphragm mechanism 14 is stopped down when the diaphragm interlocking member 14a moves upward because of the energizing spring 16 force. The rotational position of the diaphragm preset ring 13 determines a stopper 13a position. The diaphragm is able to stop-down until the interlocking member 14a contacts the stopper 13a.
In a diaphragm control mechanism as shown in FIG. 4 for example, a selection device (not shown) selects a camera shooting mode. The CPU 1 performs diaphragm mechanism control and shutter control based on the shooting mode entered. The selection device (not shown) can select at least one of a shutter priority mode, a diaphragm priority mode, a program mode, or a manual mode.
In the FIG. 4 example, when the shutter priority mode or the program mode is selected, the diaphragm is electrically stopped (enmeshed) by the CPU 1. In the diaphragm priority mode or the manual mode, the diaphragm position is determined by the preset ring 13. Therefore, only in the shutter priority mode or the program mode does the camera control the diaphragm. The control process in the shutter priority control mode is explained below.
The CPU 1 first stores in memory or the like the relationship between the number of steps of closing-in the interchangeable lens 11 and the displacement of the diaphragm interlocking member 14a.
In other words, a diaphragm operation member 17 in the camera body side (not shown) enmeshes the diaphragm interlocking member 14a in the interchangeable lens 11 side during the mounting of the interchangeable lens 11. The diaphragm operation member 17 opens the diaphragm at a determined position by opposing the energizing spring 16 force in cooperation with the energizing spring 18. As shown in FIG. 4, the energizing spring 18 has a stronger force than the energizing spring 16.
A conventional stop-down driving device (represented by reference numbers 19-22) is well known in the art. The conventional stop-down driving device interlocks with the film winding mechanism, as shown in FIG. 4.
An interlocking member 23 connects the diaphragm member 17 and a first lever 19 using a long hole 23a and a pin 23b. When the diaphragm control mode is selected, the diaphragm preset ring 13 is preferably set to the value corresponding to the smallest diaphragm diameter.
Light rays 24 passing through the open diaphragm are received by the light receiving element 25 in the vicinity of a pentagonal prism (not shown) and corresponding logarithmically compressed values are outputted from the photometry circuit 26. The output values are converted to digital values by an AD converter (A/D) in the CPU 1. The CPU 1 then computes the diaphragm value and the shutter time based on data such as film sensitivity, shooting mode, and open F-value.
In the state shown in FIG. 4, the CPU 1 detects when a release button 27 is pressed and performs control operations based on the diaphragm value and the shutter time computed at that time. In other words, the CPU 1 also functions as an exposure control device to control film exposure based on various conditions.
Control operations will now be explained. Port A is made LOW for a predetermined period of time. A transistor Tr1 magnetizes a release magnet 30 to be used for starting stop-down for the same period of time. A first enmesh lever 21 is released by the attraction force. As shown in FIG. 4, the first lever 19 rotates counterclockwise because of the spring force of an energizing spring 19a drawing the interlocking member 23 toward the right.
Then, the diaphragm operation member 17 rotates clockwise against the spring force of an energizing spring 18. Thus, the diaphragm mechanism 14 is gradually closed, corresponding to the rotation of the operation member 17.
Port B is made LOW concurrently with port A. Port B LOW causes a transistor Tr2 to turn on and supply electric power to a photo interrupter 31 with the start of stop-down. The photo interrupter 31 is an encoder for monitoring stop-down. Thus, the stop-down process is detected by a slit for encoding around the circumference of a disk 32a that rotates by enmeshing with the operation member 17. The encoding slit passes by the photo interrupter 31, which generates a pulse proportional to the amount of rotation of the disk. Hereafter, the proportional pulse is referred to as a stop-down pulse.
The stop-down pulse is received at the interruption input and the counter input (pulse cnt) of the CPU 1. When the CPU 1 detects the number of pulses equivalent to the stop-down amount necessary to adjust to the precalculated stop-down value, port C is made LOW for a predetermined time. Thus, a transistor Tr3 is turned on for the predetermined time, and a diaphragm enmesh magnet 34 is magnetized. The diaphragm enmesh magnet 34 loses attraction force against the diaphragm enmesh stop hook 35. The stop hook 35 is rotated counterclockwise from the spring force of an energizing spring 35a to stop the rotation of the disk 32a by enmeshing a gear 32b in the circumference of the disk 32a. Enmeshing the gear 32b stops the diaphragm.
The supply of electric current must be done early to offset the amount of stop-down during a delay time Td defined as the time from supply of the diaphragm enmesh magnet 34 to the diaphragm stop. Further, the generation cycle of stop-down pulses actually becomes shorter with time. The generation cycle becomes shorter because the rotation member's rotation, such as the diaphragm operation member 17, accelerates during the stop-down process of the diaphragm because of the balancing of the spring forces of the energizing springs 16, 18, and 19a.
Acceleration of the stop-down speed is not desirable. However, if the acceleration is small during the delay time Td from turning on the diaphragm enmesh magnet 34 until the diaphragm stop, significant problems are avoided. The actual delay time Td is preferably about 2 ms.
A conventional camera structure is made so that the stop-down speed is nearly uniform, and the time is detected for each stop-down pulse generated. The difference between the time of the previous stop-down pulse generated and each detected time is the pulse period. From the pulse period, a most immediate stop-down speed Vp, and the delay time Td, the number of pulses generated (hereafter, over-run pulse number, delta n) during the delay time Td is computed. When the total of delta n and an integrated value Cp of the stop-down pulses since the stop-down began equals the number of pulses equivalent to the targeted stop-down amount, current supply begins to the enmesh magnet 34.
FIG. 5 shows the structure of an electronic shutter used as a shutter mechanism.
A shutter bottom board 41 has front blade arms 44 and 45 that support freely rotating front blades 42a-42c including the shutter blades (front curtain).
As shown in FIG. 5, the front blade arm 45 is energized in the direction of the arrow by a spring (not shown). One edge section 45b is stopped by engaging with one edge of the front blade solid lever 48. The front blade solid lever 48 is supported by the shutter bottom board 41 to rotate freely. A protrusion unit 45a is formed in the front blade arm 45 to press and turn on the front blade arm running completion switch immediately before front blade running completion.
The front blade solid lever 48 is stopped by an enmesh member (not shown) and opposes the spring force of a spring 48a energized clockwise as shown in FIG. 5.
Rear blade arms 46 and 47 support freely rotating rear blades 43a-43c that form a second shutter blade (rear curtain). The rear arm 47 is energized in the direction of the arrow by a spring (not shown), but an edge 47a is prevented from rotating by enmeshing with a rear blade solid lever 49. The rear blade solid lever 49, like the front blade solid lever 48, is usually stopped by enmeshing with an enmeshing member (not shown) and opposes the clockwise force of a spring 49a.
An armature 51 is located on one edge of the front blade solid lever 48. An armature 54 is located on one edge of the lever 49. Both armatures 51 and 54 are stopped during the beginning of the shooting sequence from releasing the front curtain and the rear curtains, respectively, by supplying electric current to magnetize a transistor Tr4 and a transistor Tr5, respectively. The lever enmeshing member (not shown) releases after completion of magnetizing by a front blade driving coil MG1 and a rear blade driving coil MG2.
A magnet 53 and a magnet 56 are magnetized during electric current flow of the coils MG1 and MG2, respectively. Magnetic material is labelled 52 and 55, respectively.
When diaphragm control is complete, the CPU 1 turns off the transistor Tr4, as shown in FIG. 4, after withdrawal of a main mirror (not shown) from the light path 24 of the lens 12.
Thus, the armature 51 on the front blade solid lever 48 is released by the magnet 53 and forcibly rotates right by the spring 48a . This causes the arm 45 to begin rotating to the right by a spring (not shown), and the front blades 42a-42c begin movement clockwise, as shown in FIG. 5.
When electric current to the coil MG1 is shut off, the CPU 1 turns off the transistor Tr5 after waiting for the exposure time (shutter time) to elapse.
Then, electric current to the coil MG2 is also shut off, and the magnet 56 is demagnetized. The demagnetization of the magnet 56 causes the armature 54 and the lever 49 to rotate to the right in a similar manner as the arm 45 described above. The arm 47 begins to rotate to the right. This, in turn, causes the rear blades 43a-43c to run, and the shutter aperture 40 is closed. Complete closure of the aperture 40 turns on a switch SW4.
When switch SW4 turns on indicating exposure complete, the film winding begins. Concurrently, the various mechanisms necessary for the next shooting sequence are reset. Specifically included can be placing the shutter mechanism in the closed position, stopping the shutter mechanism by a mechanical enmeshing member, and lowering the main mirror (not shown) to the original position.
In a conventional camera, the following problems arise when using a control system with a simple power source line to conduct the shooting sequence operation, as shown in FIG. 3. The conventional camera control system is configured with the DC/DC converter 8 installed on the power source line from the battery 6. The DC/DC converter 8 continuously stabilizes the power source voltage for the entire system including, for example, during the normal shooting preparation operation time. Thus, even when the shutter time exceeds several dozen seconds, and minimal tasks are required during the film exposure like shutter time completion or detecting the exposure completion signal, the DC/DC converter 8 continuously operates.
Therefore, the conventional camera electric power consumption is very inefficient during time shooting.
Hereafter, time shooting refers to a shooting mode where exposure begins by the manual selection of the release button by the photographer, and exposure ends by a second manual selection of the release button. Alternatively, the exposure can end by photographer operation of other camera dial controls. Hereafter, bulb shooting refers to a shooting mode where exposure continues as long as the photographer engages the release button, and exposure completes when the photographer releases engagement (a finger) from the release button.
When performing time shooting and bulb shooting, a battery has high power consumption during continuous film exposure for several hours. Thus, battery power exhaustion in one night can be a major concern.
In the conventional camera when the battery charge becomes weak, the attraction power of the shutter curtain enmeshing magnet (coils MG1, MG2), for example, becomes weak during film exposure operations and causes film shooting operation problems. For example, running of the shutter rear curtain (rear blades 43a -43c) ends when the battery charge becomes weak. Therefore, a countermeasure is needed to control the camera battery consumption.